Gregory Gadow <techbear@serv.net> wrote in
news:4295D1D4.F443415@serv.net:

Grogs wrote:

Gregory Gadow <techbear@serv.net> wrote in
news:4294BDC0.5963D1B2@serv.net:

jwk wrote:

Gregory Gadow wrote:

Therion Ware wrote:

How do you lift 50,000+ tonnes to orbit?

Explode atom bombs under your spaceship.

Starting at 19:00 on BBC 4 digital the history of Orion!

I'm familiar with the concept, of course; Freeman Dyson
proposed it several decades ago. One question I've never seen
addressed, though, is what to do with the radiation?

"Do with the radiation"? What do you mean? Just stay out of its
way.

I think you have radiation confused with radioactive fallout. It
is poorly understood arguments like this that have plagued the
Orion concept for decades.

While I'm not claiming that Orion would be harmless, it just
might be less harmfull than the chemical rockets used to launch
Apollo.

My apologies for not being precise. Yes, I am referring to the
fallout.

It is my understanding that Orion technology is based on nuclear
fission. It is not enough to knock a few neutrons out of uranium
as we do in nuclear power plants; we would need much more than
just heat. Complete fission would provide both energy and reaction
matter to provide thrust. The problem is that the result of
uranium fission -- krypton and barium are most common -- are toxic
heavy metals, not to mention radioactive. Every launch would
release these atoms into our biosphere. Even relatively small
amounts would eventually build up to the point of being a major
hazard. Then there is the additional risk that an accident such as
the Challenger disaster could cause the rocket to veer over or
crash in to a populated area (killing many and leaving a
radioactive mess) or in to farmland (leaving a poisoned waste that
will be too toxic for human use for hudrends, possibly thousands
of years.) And then there is the little matter of terrorist
attacks or acts of war shooting down the rockets, not to mention
the political issues I raised earlier.

The Orion technology is talking about nuclear *bombs.* Make no
mistake about it, that is an entirely different animal than a
nuclear reactor, and I think most reasonable people would agree with
you about it being a bad idea in the atmosphere.

Which is exactly what I was saying :-) Nuclear power is generated by
knocking neutrons out of uranium. That creates a controlled chain
reaction that generates heat, which in turn is used to turn water to
steam, which is used to turn turbines to create electricity. That
process is fine if you want to boil water, but nowhere near
sufficient to power a space craft.

That all depends. Ion or plasma drives powered by nuclear reactors
would probably work quite well. The basic NERVA design was brute force
and rather inefficient.

A nuclear (fission) reactor, however, would be possible without the
significant release of radioactivity. Just as in a nuclear power
plant, water (or some other coolant) would be heated in the reactor
core. The heat from this coolant would then be transfered (through
a radiator or something similar) to the reaction mass, which would
then be forced (from the heat) out of the nozzle of the rocket. At
no point would the radioactive coolant come in direct contact with
the reaction mass, so no significant radiation would be released.
Unfortunately, since you need to shield the reactor to keep
radioactivity from escaping and even more so to make it so strong it
could survive an accident by the rocket. This technology was
explored for a time with the Nerva rockets, but never enjoyed much
success.

Because the mass of the necessary shielding eliminated the benefit of
the added thrust, making standard chemical rockets more efficient.

Fusion reaction -- converting light atoms like hydrogen in to
heavier atoms such as helium -- would be much cleaner, but I don't
believe we now have the technology to sustain a controlled fusion
reaction long enough for it to serve as a viable means of
propulsion. What fusion reactions we have managed (such as the
hydrogen bomb) still required a fusion reaction to begin the
process, which brings us back to the above arguments.

Fusion is the holy grail of nuclear engineers. We do have fusion
reactors that work wither by high temperature plasma in a very small
area or using lasers to compress a pellet of deuterium.
Unfortunately, the best we've done is near-breakeven (which is still
a very long way from producing meaningful amounts of power) and we
can only maintain the reaction for a fraction of a second. As one
scientist puts it 'we've been 15 years away from having a working
fusion reactor for the last 40 years.'

--
Gregory Gadow
techbear@serv.net
http://www.serv.net/~techbear

"I contend that we are both atheists. I just believe
in one fewer god than you do. When you understand
why you dismiss all the other possible gods, you
will understand why I dismiss yours."
-Stephen F. Roberts

On Thu, 26 May 2005 06:40:36 -0700, Gregory Gadow <techbear@serv.net>
wrote:

Which is exactly what I was saying :-) Nuclear power is generated by
knocking neutrons out of uranium. That creates a controlled chain
reaction that generates heat, which in turn is used to turn water to
steam, which is used to turn turbines to create electricity. That
process is fine if you want to boil water, but nowhere near sufficient
to power a space craft.

OTOH, a reactor, turning water into plasma, would make a very good
drive, once the ship was in space, with the added advantage that by
diverting a very small amount of the pressure, you could generate all
the electricity that your ship could ever use.

Another advantage, would be that water, methane, or anything else that
freezes at the temperatures you find out there, could be pushed ahead
as a, shield-*****-propellant-supply.

You would not reach light speed, but you might reach a significant
fraction of it, say 10%.

I recall reading somewhere that a ship, with a 1g, acceleration, and
taking time dilation into account, could reach Andromeda, and return,
in the life time of the crew.

On Thu, 26 May 2005 06:40:36 -0700, Gregory Gadow <techbear@serv.net> wrote:

Which is exactly what I was saying :-) Nuclear power is generated by knocking
neutrons out of uranium. That creates a controlled chain reaction that
generates heat, which in turn is used to turn water to steam, which is used
to turn turbines to create electricity. That process is fine if you want to
boil water, but nowhere near sufficient to power a space craft.

OTOH, a reactor, turning water into plasma, would make a very good drive, once
the ship was in space, with the added advantage that by diverting a very small
amount of the pressure, you could generate all the electricity that your ship
could ever use.

Another advantage, would be that water, methane, or anything else that freezes
at the temperatures you find out there, could be pushed ahead as a,
shield-*****-propellant-supply.